An evacuated tube panel is made up of a series of double walled vacuum tubes with a copper heat pipe running down the middle. The glass tube has a super efficient oxide coating which lets in light but stops it escaping. The heat pipe has a thimble full of liquid contained in a partial vacuum which makes the liquid boil at only 25 degrees. The steam shoots to the top of the tube, heats up the manifold and, when it has returned to its liquid state, runs back down the tube to start the whole process again.
